1. Field of the Invention
The present invention relates to methods for improving the usefulness of lymphoid cell lines as host cells for the production of proteins by recombinant DNA technology. The present invention also relates to vectors for use in such methods and to host cells produced by such methods.
2. Description of the Prior Art
Lymphoid cell lines are at present being appraised for use as host cells in the production by recombinant DNA technology of immunoglobulin molecules, related hybrid or chimeric proteins (Ig-type molecules), or other recombinant proteins. Since the lymphoid cells include myeloma cells which are of the same general type as the B cells which produce Ig molecules In vivo, it is envisaged that they will naturally possess the intracellular mechanisms necessary to allow proper assembly and secretion of Ig-type molecules. Such lymphoid cell lines may also be of use in the production by recombinant DNA technology of non-Ig-type molecules.
It is known that many lymphoid cell lines, such as myeloma cell lines and T cell lymphomas, cannot be grown in vitro on media lacking in glutamine. It has been suggested that it would be useful to be able to transform lymphoid cell lines to glutamine independence, since this may provide an advantageous method for selecting transformed cell lines.
It has been conjectured that such a cell line could be transformed to glutamine independence by incorporating therein a gene coding for glutamine synthetase (GS). Such a suggestion is made in EP-A-0 256 055 (Celltech). However, it has subsequently been found that hybridoma cell lines can generate spontaneous variants able to grow in a glutamine-free medium at such a high frequency that the identification of transfectants is difficult or impossible. For myeloma cell lines, transfection with a GS gene and growth of the transformed cells in a glutamine-free medium does not result in significant survival rates.